New way to process transparent sulfur-containing polymer film for optical devices

From left: Research team members Won-Tae Jang, Professor Sung Gab Im, Dr.Do Heung Kim, and Keonwoo Choi. Photo Credit: KAIST

Polymers have outstanding physical properties and can be easily processed in various forms, which is why they’re widely used in a variety of applications such as plastic eyeglass lenses.

But the problem is, there have been very few polymers developed so far with a so-called refractive index – which determines how much the path of light is bent when entering a material – that exceeds 1.75, and existing high-refractive index polymers require costly materials and complicated manufacturing processes.

And with the miniaturization of various optical parts used in mobile devices and imaging, demand has been rapidly growing for high refractive index transparent materials that induce more light refraction with a thin film.

Now, a research team at the Department of Chemical and Biomolecular Engineering at the Korea Advanced Institute of Science and Technology (KAIST) in Daejeon, South Korea has developed a novel technology enhancing the high transparency of refractive polymer film via a one-step vapour deposition process. The sulfur-containing polymer (SCP) film is said to exhibit excellent environmental stability and chemical resistance, which is highly desirable for its application in long-term optical device applications. The high refractive index exceeding 1.9 while being fully transparent in the entire visible range will help expand the applications of optoelectronic devices.

The research team successfully manufactured a whole new polymer thin film material with a refractive index exceeding 1.9 and excellent transparency, using just a one-step chemical reaction. The SCP film showed outstanding optical transparency across the entire visible light region, presumably due to the uniformly dispersed, short-segment polysulfide chains, which is a distinct feature unachievable in polymerizations with molten sulfur.

The team focused on the fact that elemental sulfur is easily sublimated to produce a high refractive index polymer by polymerizing the vaporized sulfur with a variety of substances. This method suppresses the formation of overly long S-S chains while achieving outstanding thermal stability in high sulfur concentrations and generating transparent non-crystalline polymers across the entire visible spectrum.

“This high-performance polymer film can be created in a simple one-step manner, which is highly advantageous in the synthesis of SCPs with a high refractive index,” said KAIST research team leader Professor Sung Gap Im. “This will serve as a platform material for future high-end optical device applications.”

Source: Korea Advanced Institute of Science and Technology